GUNPOWDER 765 



The operation of preparing the charcoal naturally divides itself into three processes : 

 1. The selection of the wood. 2. Preparation of the wood previous to carbonisation. 

 3. The carbonisation. 



In selecting the wood, care is to bo taken to avoid the old branches, as the charcoal 

 made from them would yield too much ashes. The bark is to be rejected for the same 

 reason. The wood is then cut into pieces from 4 feet to 6 feet long. If the branches 

 used are more than | of an inch in diameter, tfiey are to bo split. If the wood be 

 too large, great difficulty will be found in uniformly charring it. 



There are two methods employed in the charring of wood for gunpowder. In one, 

 the operation is conducted in pits ; but the process more commonly resorted to is 

 distillation in cylindrical iron retorts. There are certain advantages in the pit-pro- 

 cess, but they are more than counterbalanced by the convenience and economy of 

 distillation. The stills used are about 6 feet long and 2 feet 9 inches in diameter. 

 The ends of the cylinders are closed by iron plates, pierced to admit ttibes of the 

 same metal. Some of the latter are for the introduction during the carbonisation of 

 sticks of wood, which are capable of being moved to indicate the stage of the de- 

 composition, while another communicates with the condenser. The more freely the 

 volatile matters are allowed to escape, the better the quality of the resulting charcoal. 

 If care be not taken in this respect, especially as the distillation reaches its close, the 

 tarry matters become decomposed, and a hard coating of carbon is deposited on the 

 charcoal, which greatly lowers its quality. The process of burning in pits is consi- 

 dered to yield a superior coal, owing to the facility with which the gases and vapours 

 fly off. 



The degree to which the burning distillation is carried, materially influence* the 

 nature of the resulting powder. If tile operation be arrested before the charcoal 

 becomes quite black, so that it may retain a dark brownish 'hue, the powder will be 

 more explosive than it would be if it were pushed until the charcoal had attained a 

 deep black colour. When it has been found that no more volatile products are being 

 given off, the fire is damped, and in a few hours the contents of the cylinders are 

 transferred to well-closed iron boxes to cool. See CARBON. 



MIXTURE AND GRANULATION. 



A very considerable number of methods have been employed at various times, for 

 effecting that thorough incorporation of the ingredients necessary for the production 

 of a good powder. The oldest method consists in stamping the materials in wooden 

 mortars. The pestles are square shafts of wood ending in brass beaters. The 

 mortars are of wood, and so shaped that any of the composition which may be forced 

 upwards by the blows of the stampers, falls back to the bottom. In order to prevent 

 fracture of the mortars, a piece of wood of the toughest kind should be let in on the 

 spot where the pestle falls. The pestles are raised by means of cogs fixed on a shaft, 

 driven by a water-wheel or steam-engine. 



One of the many methods adopted to mix the nitre, sulphur, and charcoal, is by 

 means of drums containing metallic balls ; but this arrangement is inferior to that 

 where edge-stones are employed. This last is superior to all others, the product being 

 not only very dense and, therefore, capable of enduring, without becoming pulverulent, 

 the motion unavoidable in carrying it about ; but it is also thoroughly incorporated. It 

 is, of course, essential that the stones, and the bed on which they work, should not strike 

 fire during work. To secure this, they are sometimes made of calcareous stone, and 

 sometimes of cast iron. Previous to being subjected to the action of the mill, the in- 

 gredients must be pulverised and mixed. The pulverisation may conveniently be 

 effected in wooden drums, containing metallic balls.] The pulverised materials, after 

 being sifted or bolted, and weighed out in the proper proportions, are to be inserted 

 in a mixing drum, containing on its inside pieces of^ wood projecting inwards, so that, 

 as it revolves, complete admixture gradually takes place. The product of the last 

 operation is now ready to be laid on the bed of the mill. During the grinding, the 

 cake is kept moist by the addition, at proper intervals, 'of enough water to make it 

 cohere. As the stones revolve, a scraper causes the material to take such a position 

 that it cannot escape their action. The cake produced by the action of the stones is 

 ready for graining or corning. For this purpose the cake is subjected to a powerful pres- 

 sure, by means of a hydraulic press. The mass is then broken up and transferred to 

 a species of sieve of skin or metal pierced with holes. A wooden flail is placed on the 

 fragments, and the sieves are violently agitated by machinery. By this means the 

 grains and dust produced by the operation fall through the holes in the skin or metal 

 discs, and are afterwards separated by sifting. Sometimes the machinery is so arranged 

 that the graining and separation of the meal-powder are effected at one operation. 

 "The meal powder is re-worked, so as to convert it into grains. The next operation 



